# What is a Battery?

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Contributors: Shawn Hymel

## Usage

### Single Cell

Some circuits can be powered by a single cell, but make sure that the battery can provide enough voltage and current.

This Photon Battery Shield is being powered from a single LiPo cell

If the voltage is too high or too low for your circuit, you will likely need a DC/DC converter.

### Series

In order to increase the voltage between a battery's terminals, you can place the cells in series. Series means stacking the cells end-to-end, connecting the anode of one to the cathode of the next.

By connecting batteries in series, you increase the total voltage. Add the voltage of all the cells to determine the operating voltage. The capacity stays the same.

In this example, four 1.5 V cells are connected in series. The voltage across the load is 6 V while the total set of batteries have a 2000 mAh capacity.

In most consumer electronics that use alkaline batteries, the batteries are stacked in series. For example, this 2x AA battery holder can raise the nominal voltage to 3 V for a project.

NOTE: If you are charging lithium-ion or LiPo batteries in series, you need to make sure to use special circuitry known as a "balancer" to ensure the voltages among the cells stays even. Some chargers, like this one, have balancers to allow for safe charging.

### Parallel

If the voltage of a single cell is adequate for the load, you can add batteries in parallel to increase the capacity. Note that this also means increasing the available current (C-Rate).

Be careful when connecting batteries in parallel! All the cells should have the same nominal voltage and same charge level. If there are any voltage differences, a short circuit could occur causing overheating and possibly fire.

In this example, four 1.5 V cells are connected in parallel. The voltage across the load stays at 1.5 V, but the total capacity increases to 8000 mAh.

### Series and Parallel

If you want to increase voltage and capacity, you can combine series and parallel batteries. Once again, make sure that the voltage level is the same for the batteries in parallel, as a short circuit can occur.

In this example, the total voltage across the load is 3V, and the batteries' combined capacity is 4000 mAh.

In large battery packs, especially lithium-ion, you often see the configuration listed using 'S' and 'P' for series and parallel. The configuration for the circuit above is 2S2P. As a practical example, modern electric cars use massive arrays of batteries connected in series and parallel.